Pigments for colored paper

ABSTRACT

Compositions and methods of producing colored paper products and agents for making such products are disclosed. Surface-modified pigments can be manufactured to provide selected coloring in a paper product. The pigment can include filler particles that are bound to one or more dye components with a coupling agent, such as a silane coupling agent or a polymer such as a polycation. The pigment can also be formulated to produce a paper product with better particulate and/or fines retention, and/or higher strength by including components that can interact favorably with the fibers of a paper material. The surface-modified pigments can also be utilized to make coloring formulations such as inks for printers and other applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of a U.S. Provisional PatentApplication filed on Oct. 27, 2006 and bearing Ser. No. 60/855,023, thetext of which is incorporated herein by reference in its entirety.

The present application is also related to U.S. Patent ApplicationPublication Number US 2007/0107635 A1, bearing Ser. No. 11/501,463,filed Aug. 9, 2006, entitled “Dye-Attached and/or Surface ModifiedPigments”; and an international patent application bearing applicationnumber PCT/U.S.07/03159, filed Feb. 5, 2007, entitled “Functionalizationof Paper Components.” Both of these related applications are herebyincorporated by reference herein.

FIELD OF THE APPLICATION

The present application relates to materials and processes for modifyingpaper products, e.g., making colored paper.

BACKGROUND

Many paper and paperboard products are derived from cellulosicmaterials. The strength of these composites is due to inter-fiberhydrogen bonds, which are inherently weak and easily broken. Thus,strength additives are incorporated during some fabrication processes toincrease paper strength. These additives, and the processes that utilizethem, add steps and cost to the production.

Producing colored paper involves additional challenges. In order to makecolored paper, dyes and other ingredients are typically mixed in-lineduring the fabrication process. It is difficult to obtain consistentcolors, though, because a minimal change in dye concentration maysignificantly affect the final color of the product. Thus considerableoperator skill is required so that colors are reproducible across lots.In addition, dyes will impart color to the processing equipment during agiven dye run, so that changing from one color lot to another must bepreceded by an elaborate cleaning protocol that is time-consuming andexpensive. There remains a need in the art for products and processesthat reduce costs, increase efficiency, and decrease waste whileincreasing paper strength and optimizing color.

SUMMARY

Some embodiments are directed to a paper product, such as a coloredpaper product. The paper product can include pulp comprising a pluralityof fibers (e.g., cellulosic-based fibers and/or other fibers used inpaper products). Surface-modified pigment particles can also beincluded. Such particles can impart a selected color to a paper product.Surface-modified pigment particles can include a filler particle, whichcan be embedded with the pulp. A coupling agent can be used to bind oneor more dye components and the filler particle together. Fillerparticles can include one or more of a biopolymer, a bio-oligomer, metaloxide, silaceous material, and calcium carbonate. Filler particles,which can optionally be nanoparticles or other sized particles, canalso, or alternatively, include an inorganic surface such as calciumcarbonate, kaolin, titanium dioxide, or combinations thereof. Suchparticles can comprise sites attached to the coupling agent by reactionof a hydroxide group on the particle surface. In some embodiments, thecoupling agent is directly bound to the filler particle by at least oneof covalent bonding, non-covalent bonding, electrostatic forces, Van derWaals forces, hydrogen bonding, and intermolecular forces.

Dye components can be adapted to provide the selected color to the paperproduct, and can include any appropriate material for impartingcoloration to paper. In some embodiments, the dye component can be anyof halogenotrizine, carboxypyridinium-substituted triazine,trihalogenopyrimidine, dichloroquinoxaline, vinyl sulfone, halotriazine,anthraquinone-like structure, azo dye, triaryl dye, metal complex, andcombinations thereof. The dye component can also include any combinationof a fluorescent dye, a phosphorescent dye, a photochromic dye, athermochromic dye, a FD&C dye, a whitener, a brightener, a lightstabilizer, and a ultraviolet light stabilizer.

Coupling agents for use with embodiments disclosed herein can be in avariety of forms and interact with the surface-modified pigmentparticles in a variety of manners. For instance, the coupling agent(s)can use one or more intermediary agent(s), which can couple the couplingagent to the particle, or can couple another component (e.g., one ormore dye components) to the coupling agent, or both. In someembodiments, the coupling agent comprises a multifunctional couplingagent or a polymer. In some embodiments, a coupling agent can include asilane group that can react to attach to a filler particle eitherdirectly or indirectly. Coupling agents can also, or alternatively,include a reactive group including at least one of amine, thiol, epoxy,isocyanate, or hydroxyl; the reactive group reacted to attach to thefiller particle. In some embodiments, the coupling agent can comprise apolymer, such as a polyelectrolyte (e.g., a polycationic polymer).Examples of polycationic polymers include any combination ofamine-containing polymers, such as chitosan, polyalkyleneimine,polyvinyl amine, and polyallyl amine, and a cationic starch. An anioniccomponent can also be added such as to couple together with thepolycation. The anionic component can be adapted to bind the anioniccomponent and one or more dye components, or other components, togetherso as to couple such components to the filler particle. Examples ofanionic components can include anionic polymers or a coupling agent thatcan optionally include a silane group.

In some embodiments, the surface-modified pigment particles can be boundtogether with other paper components, such as a fiber of the paper'spulp. For instance, the coupling agent (e.g., an amine-containingpolymer such as chitosan) can act to bind a filler particle and a fiberdirectly or indirectly together. In another instance, a functionalizingagent, such as a polymer, can be included with a surface-modifiedpigment particle to aid binding of the particle (or components thereof)and a fiber together. A functionalizing agent (e.g., polymer) can beattached together with the coupling agent and/or can be directlyattached together with a filler particle. The attachment can be bycovalent bonding, non-covalent bonding, electrostatic forces, Van derWaals forces, hydrogen bonding, intermolecular forces, and combinationsof such named mechanisms, among others. Examples of functionalizingpolymers include an amine-containing polymer, a glycoaminoglycan, anamino-containing polymer, and an imine-containing polymer.

Other embodiments of the invention are directed to slurries that can beused to make paper products such as colored paper products. The slurrycan include an aqueous medium, which can be used to disperse the otherpaper components. Other components can include pulp having a pluralityof fibers, and a surface-modified pigment mixture. Such a mixture, whichcan be used to impart a selected color to a paper product, can includefiller particles, one or more dye components, and a coupling agentadapted to bind the dye component(s) and the filler particles together.The components of such slurries, such as the surface-modified pigments,pulps, filler particles, dye components, and coupling agents, caninclude any of such components as disclosed herein.

Additional embodiments of the invention are drawn to surface-modifiedpigment, and formulations that utilize such pigments such as inkformulations that are dispersed in an aqueous medium. Surface-modifiedpigment particles can include a plurality of pigment particles having afiber affinity component, such as a polycation, coupled together withthe pigment particle. The fiber affinity component, such as apolycation, can act to bind the particles with the fibers of apaper-based material. For example, when used in an ink formulation, apolycation can act to improve binding between the ink formulation andthe paper relative to not having the polycation in the ink formulation.Though a variety of pigment particles can be utilized, in someembodiments the surface-modified pigment particles can be comprised offiller particles having one or more dye components bound together with acoupling agent (e.g., a polycation). The types of surface-modifiedpigment particles that can be utilized, and the components of suchparticles, include the variety of types and components disclosed herein.

Further embodiments are drawn toward methods of producing a coloredpaper product. A surface-modified pigment can be produced by bindingfiller particles and one or more dye components together using acoupling agent such as a polymer or a material having a silane group.For example, the filler particles can be encapsulated with a polycation,where the polycation can be attached using the coupling agent or thepolycation can be the coupling agent itself. The surface-modifiedpigment can be combined with pulp comprising fibers so as to produce apapermaking dispersion. A colored paper product can be then be formedfrom the papermaking dispersion.

In some of the method embodiments, the filler particles can bind to afiber of the dispersion, which can result in a stronger final paperproduct and/or increased retention of fillers (and associated componentsthereof) and/or fines. As well, the color of a paper product can beadjusted by selecting the relative amount of coupling agent to dyecomponent(s). Anionic components can be bound to a polycation to provideadditional functionality, for example.

The steps of producing the surface-modified pigment and combining thepigment with pulp can be practiced sequentially, or substantiallysimultaneously (e.g., a mixture of components to become thesurface-modified pigment can be combined with the fibers to make areacting papermaking dispersion). As well, portions of asurface-modified pigment particle can be manufactured and coupledtogether with a filler particle, or other paper components such asfibers, before remaining portions of the pigment particle are completed.Alternatively, or in addition, the surface-modified pigment can beassembled in a variety of manners, e.g., a dye component can be coupledtogether with a polycation before the polycation encapsulates (such asby self assembly upon the surface) a filler particle, or the dye can becoupled after the polycation is attached to a filler particle.

BRIEF DESCRIPTION OF THE FIGURES

The objects and features disclosed in the present application can bebetter understood with reference to the drawings described herein, andthe claims. The drawings are not necessarily to scale, emphasis insteadgenerally being placed upon illustrating one or more principles of theinvention. In the drawings, like numerals are used to indicate likeparts throughout the various views. While the invention is particularlyshown and described herein with reference to specific examples andspecific embodiments, it should be understood by those skilled in theart that various changes in form and detail may be made therein withoutdeparting from the spirit and scope of the invention.

FIG. 1 illustrates schematically a system for attaching a reactive dyeto a particle, consistent with an embodiment of the present invention.

FIG. 2 illustrates schematically a system for attaching a reactive dyeto a coated particle, consistent with an embodiment of the presentinvention.

FIG. 3 illustrates schematically another system for attaching a reactivedye to a coated particle, consistent with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the invention are drawn to various aspects ofpapermaking, such as improving engineering properties of paper-basedmaterials, improving the process efficiency of such operations,imparting color or other appearance features to paper-based materials,and/or decreasing waste production during papermaking operations. Insome embodiments, processes and materials used in paper manufacturingutilize surface-modified filler particles to achieve changes inproperties of the resulting paper-based material. Several embodimentsutilize surface-modified pigment particles to impart a selected color ina paper-based material, for example either throughout the paper and/orwhen such surface-modified pigment particles are used in an inkformulation.

In some embodiments, the surface-modified pigment particles can comprisefiller particles that can have one or more dye components that are boundtogether with the filler particle using a coupling agent. A dyecomponent can be selected to impart a desired coloration to theparticles, and hence a paper-based product. Such embodiments arepotentially advantageous in reducing wasted use of dyes during paper orink production. Since dyes are typically liquid-based materials that aresoluble in a papermaking mixture, excess dye is often used in colorationof paper components. By using a surface-modified pigment, where theparticles are not soluble in the papermaking mixture, loss of colorationmaterials can be reduced. In other embodiments, a surface-modifiedpigment particle can include a polyelectrolyte bound to the particlesurface. Such polyelectrolytes can be adapted to bind together withfibers (e.g., cellulose-based fibers) of a paper or paper mixture, whichcan result in enhanced properties such as paper strength. These aspectsand others are discussed in further detail herein.

DEFINITIONS

Unless the context of use suggests otherwise, the following definitionsapply to the terms and phrases used throughout the present application.

The terms “a” and “an” are interchangeable and are the same as thephrase “one or more.”

The terms “attach,” “bind,” and “bound” are synonymous with each otherand refer to a coupling between entities. Such coupling can either bedirect, such as a polymer sharing a covalent chemical bond with asurface site of a particle together, or can be indirect, such ascoupling a polymer and a surface site together using an intermediaryagent which is directly coupled to the polymer and the surface site(e.g., a bifunctional coupling agent). Binding between entities canoccur by any feasible mechanism consistent with an embodiment of theinvention. Accordingly, non-limiting mechanisms by which chemicalentities can be bound together include covalent bonding, non-covalentbonding, electrostatic (or ionic) forces, Van der Waals forces, hydrogenbonding, other intermolecular forces, and combinations of the listedmechanisms.

The phrase “pigment particle” refers to one or more particles that areused to impart coloration. A pigment particle can be based from organicand/or inorganic materials, and can be chosen to be insoluble in a givenmedium, such as an aqueous solution and/or a mixture from which papercan be manufactured.

The term “polymer” refers to a molecule comprising a plurality of repeatunits or monomers. A polymer can comprise one or more distinct repeatunits. For example, a “copolymer” refers to a polymer having two or moredistinct repeat units. Repeat units can be arranged in a variety ofmanners. For example, a homopolymer refers to a polymer with one type ofrepeat unit where the repeat units are adjacently connected. In anotherexample, a plurality of different repeat units can be assembled as acopolymer. If A represents one repeat unit and B represents anotherrepeat unit, copolymers can be represented as blocks of joined units(e.g., A-A-A-A-A-A . . . B-B-B-B-B-B . . . ) or interstitially spacedunits (e.g., A-B-A-B-A-B . . . or A-A-B-A-A-B-A-A-B . . . ), or randomlyarranged units. Of course, these representations can be made with 3 ormore types of repeat units as well. In general, polymers (e.g.,homopolymers or copolymers) include macromolecules in a broad range ofconfigurations (e.g., cross-linked, linear, and/or branched). Thepolymer can be disposed in a variety of mixture dispositions such assolutions, melts, and/or gels. A gel refers to a state where a mixtureof polymer and liquid has at least some properties that make the mixturebehave more like a solid than a viscous liquid (e.g., the mixtureexhibits elasticity). A polyelectrolyte refers to a polymer where one ormore of the repeat units includes an ionic group. Accordingly, suchgroups can be charged in an aqueous solution. When the ionic groupsinclude a cationic group, the polyelectrolyte can be referred to as a“polycation.” When the ionic groups include an anionic group, thepolyelectrolyte can be referred to as a “polyanion.” In some instances,the polyelectrolyte can also have a net zero charge.

Colored Paper Products

Some embodiments are directed to paper products, and in particular paperproducts with a selected color. Paper products include the range ofpaper, paper-board, and other paper-based materials that can bemanufactured. In some instances, the paper product can include pulp inthe form of a plurality of fibers and surface-modified pigment particlesfor imparting color to the paper product. The surface-modified pigmentparticles can include filler particles, such as those typically utilizedin paper manufacturing (e.g., inorganic particles like precipitatedcalcium carbonate (herein “PCC”) or silicon dioxide). One or more dyecomponents can also be included, which can be bound together with one ormore of the filler particles using one or more coupling agents. In someembodiments, the dye can be durably, if not substantially permanently,bound together with the filler particle (e.g., the dye can besubstantially attached to, and remains unremoved from, a filler particleduring a papermaking process). Thus, such embodiments can advantageouslyreduce the loss of excess dye components inherent when excess solubledye liquid is employed for paper coloration. In addition, suchembodiments can potentially produce a richer set of pigments for usewith paper that correspond with useable dyes.

Other embodiments can be directed to slurries, or other types ofmixtures of components, that can be used to form paper products (e.g.,paper products with a selected coloration). The slurry often timesincludes an aqueous medium, though non-aqueous mediums and mixed mediasystems (e.g., surfactant can be present to form micelles) can also beutilized. The slurry can include pulp having a plurality of fibersdispersed in the medium. A mixture for producing surface-modifiedpigments can also be included in the slurry. Such a mixture can includefiller particles and one or more dye components for selectively coloringthe filler particles. A coupling agent can also be present in themixture. The coupling agent can be chosen to bind the dye component(s)and the filler particles together. Thus, in some embodiments, thesurface-modified pigment mixture can impart a selected color to a paperproduct formed from such slurries.

More detailed descriptions of particular aspects of embodiments of paperproducts and slurries are discussed herein. It is understood that theseaspects are individually or combinatorially interchangeable, and can beadditionally inserted, or deleted from, various embodiments of theinvention. For example, the use of a particular aspect of a couplingagent in a paper-forming slurry can also be used in a resulting paperproduct, regardless of whether it is explicitly stated in the presentapplication. In another example, more than one type of coupling agentcan be employed in an embodiment where the coupling agent can beselected from any of the coupling agents disclosed herein. Indeed, thoseskilled in the art will recognize that minor changes and modificationsof disclosed aspects of the invention can be performed without undueexperimentation. All such variations are within the scope of the presentapplication.

Component Descriptions

Paper products and slurries for making such products, among otherembodiments, can utilize pulps that are typically utilized inconventional paper manufacturing. Thus, the pulp utilized in someembodiments disclosed herein can comprise fibers such as cellulose-basedfibers, and can also include other components typically found inpulps/fibers used to make paper products (e.g., filler additives). Inmany embodiments, the fibers of the pulp can have a net negative charge.Such net charge can be utilized advantageously in some embodiments tocause electrostatic attraction of cationic moieties such as polycations.Though any type of compatible fiber material can be utilized in a pulp,in some embodiments the fibers of a pulp exclude the presence ofsynthetic fibers such as polymer-based fibers (e.g., aromatic amidefibers). Thus, some embodiments utilize pulps that include substantiallynaturally-occurring fibers. Other embodiments, however, can utilizepulps that include synthetic fibers such as polymer-based fibers (e.g.,aromatic amide fibers) or other types of synthetic fibers.

As well for papermaking purposes, filler particles can be made intosurface-modified pigments (e.g., colored pigments), can be used inunmodified form, or can comprise a mixture of modified and unmodifiedparticles, which can be used in various embodiments described herein.Such filler particles can comprise any number of materials. Non-limitingexamples include polymers, biopolymers, bio-oligomers, metal oxides,calcium carbonate silicas, inorganic components, and mixtures of suchmaterials. Particles commonly used in the paper industry include thosemade from materials such as kaolin, calcium carbonate, and titaniumdioxide; such particles can also be used with the embodiments disclosedherein. In particular embodiments, the filler particles have a surfacecomprising one or more the listed materials herein. For instance, fillerparticles with an inorganic surface (e.g., metal oxide surface) can beused in particular embodiments to bind together with selected couplingagents. The selected coupling agents can aid in binding a dye componentor some other component (e.g., a functionalizing polymer such as anamine-containing polymer to aid binding of a surface-modified pigment topulp fibers) to improve interactions with pulp fibers or to add otherbeneficial properties such as enhanced pigment particle, other fillercomponents, and/or fines retention. For example, the coupling agent canattach to the particle surface via a reaction with a hydroxide grouppreviously residing on the particle surface or as part of the unreactedcoupling agent. In some embodiments, filler particles can have a netnegative charge on their surfaces for binding with cationic entitiessuch as polycations.

In embodiments, filler particles may be of any shape, includingsubstantially spherical, amorphous, cylindrical, plate-like, flake-like,or any other geometry. Particles may be selected for physical propertiesdesirable in papermaking, including porosity, strength, opacity, orother characteristics. In embodiments, the particles may have averagedimensions from 3-200 microns, or from 5-100 microns; in someembodiments the average dimension (e.g., diameter, radius, or effectivedimension based on some type of surface area measurement) can be theaverage of the largest dimension of the particles. In embodiments, theparticle may be a nanoparticle. As used herein, the term nanoparticleapplies to a particle having at least one dimension measuring less than100 nm on average. It is understood that while embodiments herein referto surface-modified filler particles that include a bound dye component,dye components can also be bound to other substrates to formsurface-modified substrates to form a surface-modified pigment (e.g., acoating material), which can be used to replace surface-modified pigmentparticles in some embodiments described herein.

In embodiments, one or more dye components can be bound to one or moresubstrates (e.g., filler particles) to produce a manufactured colorant.As discussed in the present application, a dye component refers to acolorant, which can be bound to a filler particle or other substrate toform a surface-modified filler particle. In some embodiments, a dyecomponent can be a reactive dye. As used herein, the term “reactive dye”refers to a chromophore containing one or more moieties that is/arecapable of reacting with, or otherwise binding to, a substrate, such asa fiber or a particle. Some dye components can include a vinyl sulfone.In certain embodiments, the dye component can include a halotriazine,for example, a chlorotriazine. In embodiments, the dye component caninclude one or more of the following: a monohalogenotriazine, adihalogenotrizine, a carboxypyridinium-substituted triazine, atrihalogenopyrimidizine, and/or a dichloroquinoxaline. The dye componentcan also include a fluorescent dye, a phosphorescent dye, a photochromicdye, a thermochromic dye, a whitener, a brightener, a light stabilizer,and/or a ultraviolet light stabilizer. Anionic dyes can also be utilizedas a dye component. Anionic dyes include acid dyes having a variety ofstructures, for example anthraquinone-like structures, azo dyes, triaryldyes, and metal complex dyes. Other anionic dyes include Food, Drug, andCosmetic (herein “FD&C”) dyes, which are approved for use in foods,drugs, and cosmetics subject to U.S. Food and Drug Administrationregulations.

Coupling Agents and Functional Groups

In embodiments, surface modified pigments and surface modificationprocesses described herein can include the use of a variety of types ofcoupling agents to bind one or more dye components or other components,and filler particles or other substrates together. It is understood thatcoupling agents can act to bind dye component(s) and filler particles ina variety of configurations. For instance, the coupling agent can bedirectly bound to the filler particle and dye component to causecoupling. In another instance, one or more intermediary components canbind the particle and coupling agent together, with a dye componentdirectly bound to the coupling agent. In yet another instance, one ormore intermediaries can bind the dye component(s) and coupling agenttogether, with the coupling agent directly bound to the particle. Otherinstances can use intermediaries, same or different, to connect thecoupling agent and dye component, and the particle and coupling agent.It is also understood that while many embodiments specifically discusscoupling of dye components, other components can also be bound withcoupling agents. These variations and others, including ones understoodby a skilled artisan, are all within the scope of the present invention.

In some instances, a multifunctional coupling agent can be employed tofunctionalize a filler particle to bind a dye component or othermaterial (e.g., a polycation) thereto. As used herein, the phrase“multifunctional coupling agent” refers to agents which include at leasttwo distinct types of functional groups that can be used to bind toother entities (e.g., a filler particle surface and/or a dye component).Examples of multifunctional coupling agents include an agent with asilicon atom or silane group for direct linkage to the surface of afiller particle or other substrate. The multifunctional coupling agentcan be a small-molecule, an oligomer, or even a polymer.

Though much of the following description is with reference to functionalgroups on a multifunctional coupling agent, it is understood that suchgroups can be utilized on other coupling agents as well. Indeed, suchgroups can be utilized on other coupling agents within the scope of thepresent application.

In some embodiments, the multifunctional coupling agent can include asilicon-containing group and at least one other different type offunctional group. Examples of other functional groups include an aminegroup, an amino group, an epoxy group, a hydroxyl group, a thiol group,an acrylate group, a carboxyl group, and/or an isocyano group. In oneembodiment, the silicon-containing group can be a silane group.Instances of such groups can include an isocyanosilane, for example, atrialkoxy isocyanosilane such as trimethoxy isocyanosilane, triethoxyisocyanosilane, and/or triisopropoxy isocyanosilane. In certainembodiments, the multifunctional coupling agent may include anaminosilane, for example, a trialkoxy aminosilane such as triethoxyaminopropylsilane and/or trimethoxy aminopropyl silane. In certainembodiments, the multifunctional coupling agent may include an epoxysiloxane. The coupling agent can include triethoxy methacryloxypropylsilane. Though in many instances a multifunctional coupling agent isembodied as a bifunctional coupling having one silane group and oneother group, it is understood that a multifunctional coupling agent canhave one or more silicon-containing groups, and/or one or more otherfunctional groups. It should also be understood that certain embodimentsof multifunctional coupling agents need not include a silicon atom or asilane group.

To illustrate some aspects of the invention, a multifunctional couplingagent can bond with the surface groups on filler particles, and can haveone or more functionalities, which can be located on a free end, thatcan connect with a dye component. For instance, a bifunctional couplingagent can have one group that can react with the surface of a fillerparticle and a different group that can react with a reactive dyecomponent. In one example, when a filler particle having a metal oxidesurface is utilized, a multifunctional coupling agent can include ahydrolysable silane or hydroxyl silane as one group to react with themetal oxide surface. An amine, thiol, epoxy, isocyanate, or hydroxylgroup can be used as another group to bind a reactive dye to theparticle. For instance, an alkoxy, halo, hydroxyl, or other group on thesilane can form a bond with the particle surface. The other group can beon another end of the coupling agent to react with the reactive dye.Moieties including, but not limited to, a primary amine, a secondaryamine, and/or an alcohol group, may react to a dye containing achlorotriazine.

Though in the above illustration covalent bonding can cause connectionof a functional group of a coupling agent with a particle surface and/ordye component, it should be understood that the functional group of amultifunctional coupling agent can induce binding by other mechanisms aswell. The functional group can covalently link the dye to the particlesurface; alternatively, the linkage may be non-covalent, ionic (e.g.,electrostatic forces), or via Van der Waals forces, hydrogen bonds,and/or other intermolecular forces.

FIG. 1 depicts schematically an illustrated embodiment of the invention.As shown, a filler particle 12 according to compositions and methodsdescribed herein can be attached to a coupling agent 14, with a linkage30 formed between the coupling agent 14 and the particle 12. Thecoupling agent 14 can include a free end 18, providing a site forattachment of a reactive dye 20. As illustrated, the reactive dye 20 caninclude a chromaphore 22 and a reactive moiety 24. The reactive moiety24 of the reactive dye 20 can attach to the free end 18 of the couplingagent 14, forming a linkage 28 that attaches the reactive dye 20 to theparticle 12 via the coupling agent 14.

While in some embodiments a dye component can directly bind with amultifunctional coupling agent, in other embodiments the dye componentcan be bound to a coupling agent through one or more intermediaryentities. For example, the number of amine groups on a particle surfaceavailable for reaction with a dye component (or even other types ofcomponents) can be increased by using a coupling agent with a functionalgroup that reacts with amines and first attaching an amine-containingpolymer to the coupling agent for subsequent reaction with the reactivedye. For instance, a polyamine such as chitosan, branchedpolyethylenimine, or polyallyl amine can be reacted onto an isocyano orepoxide group of a multifunctional coupling agent (that is attached tothe particle) for subsequent reaction to a reactive dye. In anotherinstance, a number of alcohol groups available for dye interaction canbe enhanced. In one example, a cellulosic polyanion can be attached to afiller particle surface with alcohol moieties using a multifunctionalcoupling agent including acid groups capable of reacting with thealcohol groups on the particle surface. Hydroxyl groups of the polyanioncan be reacted with a reactive dye to complete the surface-modificationof the particles. It is understood that a coupling agent can be adaptedto bind with components other than a dye component to provide additionalfunctional advantages in a paper-based product. For instance, whenchitosan is bound to a filler particle using a coupling agent, the freeamines can be used to interact with the fibers of a paper product, asopposed to binding with a dye component, to increase the retention ofthe filler particle and/or fines, which can increase the strength of aresulting paper material.

In some embodiments, a second multifunctional coupling agent, which canbe distinct from a first multifunctional coupling agent, can be utilizedto bind another component to a filler particle, such as a different typeof dye component or a polymer for enhancing paper component strength orproperties (e.g., hydrophobicity). Such a second multifunctionalcoupling agent can utilize any of the binding mechanisms previouslydiscussed, such as covalent, non-covalent, ionic, or via Van der Waalsforces, hydrogen bonds, and/or other intermolecular forces. It is alsopossible that no second coupling agent is utilized. In such an instance,moieties of the additional component bind to moieties of the firstmultifunctional coupling agent, or bind directly with moieties on afiller particle surface. The moities on the particle surface can eitherbe inherent to the surface, or the surface can be modified in some otherfashion. It is also contemplated that additional multifunctionalcoupling agents can also be used with various embodiments of the presentinvention.

While some embodiments herein contemplate the use of a multifunctionalcoupling agent that can bind directly with a surface of a fillerparticle, practice of the invention is not necessarily limited to suchembodiments. Some instances can utilize a filler particle that includesa coating layer on the particle's surface. A multifunctional couplingagent, which can be bound to a dye component or other component, can beattached to the coating layer, thus providing the connection between thecomponent and the filler particle. FIG. 2 provides one specificillustration of this arrangement.

As depicted in FIG. 2, a coating layer 116 can be deposited onto thesurface of a particle 112, forming a coated particle 110. Methods fordepositing the coating layer 116 onto the particle 112 may includeelectrostatic interaction, spray drying, precipitation, or chemicalreaction involving covalent, non-covalent, ionic or van der Waalsforces, or the like. Many methods for depositing the coating layer 116will be familiar to skilled artisans. The coating layer 116 can thenprovide a nexus for attachment 130 of a coupling agent 114. The couplingagent 114 can have a free end 118 that permits attachment of a reactivedye 120. The reactive dye 120 can comprise a chromaphore 122 and areactive moiety 124. As shown in FIG. 2, the reactive moiety 124 canattach to the free end 118 of the coupling agent 114, thereby forming alinkage 128. In some embodiments, the reactants can be reactedsequentially, for example, so that the coating layer 116 is firstdeposited on the particle 112, followed by the deposition of thecoupling agent 114, followed by the attachment of the reactive dye 120to the coupling agent 114 free ends 114. In other embodiments, some orall of the reactants may be mixed together initially, with the productsof these mixtures then being reacted together.

In some embodiments, a coating layer can comprise one or more layers ofpolymers. For example, amine-containing polymers can be directlydeposited onto a particle surface without the use of an intermediary, atechnique useful for many types of particles, including calciumcarbonate and metal oxides. Amine-containing polymers useful for thistechnique may include a number of polymers containing primary orsecondary amines. Examples include chitosan, branched polyethylenimine,linear polyethylenimine, and polyallyl amine. Other aspects ofamine-containing polymers discussed elsewhere within the presentapplication can also be incorporated. To accomplish the direct depositof an amine-containing polymer onto the surface of the particle, anumber of methods may be used, including electrostatic interaction,spray drying, or precipitating the polyamine out of solution onto theparticle by adjusting the pH. For example, chitosan may be depositedonto a particle by slowly raising the pH until chitosan is insoluble. Itis understood that a variety of components can be linked to a coatinglayer beyond a coupling agent. For example, in some instances a reactivedye can be coupled to one or more free amines of the polyamine withoutthe use of a coupling agent. Other components include polyanions orother groups capable of binding with an amine group, for example.

In other embodiments, a surface-modified substrate (e.g., fillerparticle) can include a multifunctional coupling agent and afunctionalizing component, where the functionalizing component binds tothe surface of the filler particle. Though the functionalizing componentcan bind to the surface using an intermediary such as a multifunctionalcoupling agent, in some embodiments the functionalizing component bindsdirectly to the surface of the filler particle. Such functionalizingcomponents can serve to enhance the properties of a resultant paperproduct in terms of its appearance, strength, and/or other properties.In some embodiments, the functionalizing component can be one or morefunctionalizing polymers. Such polymers can include any of the polymersdescribed herein that can act as a coupling agent, for example. In oneinstance, the polymer can be a polycation such as an amine-containingpolymer, a glycoaminoglycan, an amino-containing polymer, and animine-containing polymer. Such polymers can be advantageous since theamine groups can act as sites of interaction, allowing the binding ofentities such as reactive dyes to further enhance pigment colorationabilities, or fibers of a paper pulp to enhance the overall strength ofthe paper material.

Polymeric Coupling Agents

In some embodiments, the coupling agent can be a polymer, such as apolyelectrolyte (e.g., a polycation). Polymer coupling agents can differfrom multifunctional coupling agents in that the polymer may not have aplurality of different functional groups to bind with various entities,though polymers with multifunctional groups for binding can also beutilized. In some embodiments, the polymer coupling agent can bind tothe surface of a filler particle directly. Such binding can occur by anynumber of mechanisms such as electrostatic forces, Van der Waals forces,covalent bonding, or other intermolecular forces. For example, thepolymer can include silane groups (or other silicon-containing groups)capable of binding to a filler particle surface (e.g., having a metaloxide surface) by reacting with a surface site. In another example, apolycation with amine-containing groups can bind with a negativelycharged surface of a filler particle. One or more dye components, and/orother components, can also bind with the polymer to create bindingbetween the component(s) and the filler particles.

A variety of polymers can be utilized as a coupling agent. In someembodiments, the polymers can have an amine group, an amino-group, animine group, or a combination of such groups. Other polymers can includehydroxyl groups, where entities can be attached at the hydroxyl sites.Particular embodiments utilize polycations as a coupling agent. Suchembodiments can be beneficial for creating binding with substrates andparticle surfaces that have a net negative charge. Accordingly, someembodiments can advantageously utilize polymers that are polycationic(e.g., amine-containing polymers such as chitosan).

In general, amine-containing polymers (also referred to as polyaminesherein) for use with compositions and methods disclosed herein includeat least one primary (—NH₂), secondary (—NHR₂), and/or tertiary amine(—NR₃) group. Such polymers can also, or alternatively, include aquaternary ammonium cation or a quaternary ammonium salt moiety. Theamine groups of an amine-containing polymer can include charged and/oruncharged groups. Examples of amine-containing polymers can includechitosan, polyalkyleneimine, polyvinyl amine, and polyallyl amine. Insome embodiments, a surface-modified pigment particle with an attachedpolymer can be treated or washed with an acidic solution or compound,such as an acidic solution comprising an inorganic acid, to create acharged group (e.g., an amine group) and/or a stable salt complex. Suchpolymers can be in the form of an amine salt, and may include saltsformed with formic, acetic, succinic, citric, lactic, maleic, fumaric,palmitic, cholic, pamoic, mucic, d-glutamic, d-camphoric, glutaric,glycolic, phthalic, tartaric, lauric, stearic, salicyclic,methanesulfonic, benzenesulfonic, paratoluenesulfonic, sorbic, puric,benzoic, cinnamic and the like organic acids. A particular polymer canbe in the form of an amine hydrochloric acid salt. An acidic solutionfor use can be at a concentration that facilitates the formation of thecharged amine group, but may not be at a concentration that would removethe amine group or other moieties from the polymer.

Examples of polymers for use in compositions and methods disclosedherein can include glycoaminoglycans such as polysaccharides, gums,starch or cationic derivatives thereof, that include an amine group. Forinstance, such polymers can include chitosan, hyaluronic acid,chrondoitin sulfate, and certain proteins or polypeptides. As usedherein, “polysaccharide” is understood to mean a biological polymerhaving sugar subunits, for example, a starch or a cellulose, or aderivative of such a biological polymer; chitosan, pectin, orcarboxymethyl cellulose are specific examples.

Other polymers for use in these systems and methods includepolyalkyleneamines (PAA) such as tetrabutylenepentamine,polyalkyleneimines (PAI), polyethyleneamine (PEA) such astriethylenetetramine (TETA) and teraethylenepentamine (TEPA), andpolyethyleneimines (PEI) such as linear polyethyleneimine (LPEI),branched polyethyleneimine (BPEI), polyallylamines, and polyvinylamines.Branched polyethylenimine, for example, may have at least moderatebranching. In certain embodiments, film-forming polymers are used, whichcan facilitate attachment of the polymer onto the particles (e.g.“wrapping” of the polymer onto the particles). Still other polymersuseful in these systems and methods can include poly(amido-amine)dendrimers, poly(alkylamino-glucaramide), and linear polymers with asingle primary, secondary or tertiary amine group attached to thepolymer units, such as poly(dimethylaminoethyl methacrylates),dimethylamino dextran, and polylysines.

In some embodiments, a natural or synthetic polyelectrolyte can be usedas a coupling agent where the polyelectrolyte includes one or moresilicon-containing groups (e.g., silane groups). For example, thepolyelectrolyte can include an aminosilane polymer, which can optionallybe dispersed in an aqueous medium. The silane groups can allow thepolyelectrolyte to bind to the filler particle, and the amino groups caninduce binding with one or more dye components (e.g., by reacting with areactive dye). The resultant surface-modified pigment particles canserve as pigments that can be used to change the color of a resultingpaper product. The new pigment made according to these methods can alsoretain residual functional groups (e.g., amine groups) by not saturatingthe coupling agent with dye molecules. The remaining amine groups canact to bind with fibers of a paper pulp to enhance the strength and/orweight of a resulting paper product.

Polymers (e.g., polycations) that contain hydroxyl groups for dyereaction can also be attached to reactive dyes or other components, ascan cationic polymers where the amines are left free to preserve thecationic nature of the polymer (either using stoichiometry or doing thereaction while the amine is charged). The dyed polycation can then becoated onto the particle surface directly using electrostaticinteractions or by precipitation. The dyed polycation may also becoupled to the surface of the particle using a coupling agent.Multilayers of dyed or undyed polycations, and dyed or undyed polyanionscan be built on the surface if desired to deepen the color of theparticle through sequential addition of the polycations and polyanions.Embodiments using multiple layers of polycations and polyanions canenhance the amount of polyelectrolyte available for interacting withother entities (e.g., by increasing the surface area available).

In some embodiments where a polymer acts as a coupling agent, thepolymer can attach to surface sites of the filler particle in a sparsemanner, or can be attached in a manner that the polymer can encapsulatethe filler particle. For example, when applied to papermaking,techniques for encapsulation of filler particles with polycations(natural or synthetic) can involve such methods as slowly precipitating,spray drying, or using any known encapsulation technique to coat thepolycation onto the particle. Using the techniques described herein, orusing other techniques including those familiar to skilled artisans,additional polyelectrolytes can be added to further increase theperformance properties of the paper or help balance the charge of thepaper stock. For example, this can be done by further encapsulating theparticle or adding it to the stock slurry.

In embodiments where a filler particle can use a polymer as a couplingagent, a dye component (e.g., a reactive dye) can be attached to thepolymer to form a surface-modified pigment particle. In someembodiments, the dye component is directly attached to the polymercoupling agent without any other intermediary component, such asreacting at an amine site of an amine-containing polycation. Such a dyecomponent can be bound to the polymer before the polymer is bound to thefiller particle, after the polymer is bound to the filler particle, orduring a process in which all components are mixed in a reaction brothand binding of the components occurs substantially simultaneously. Withthe use of an anionic dye component, binding to a polycationic couplingagent can be performed through the electrostatic interactions betweenthe dye and polymer. Multiple layers of polycations and anionic dyes canbe used to deepen the color of the particle.

FIG. 3 schematically illustrates particular embodiments of theinvention. As shown, a polymer-bound dye 210 may be formed by combininga reactive dye 220 comprising a chromophore 222 and a reactive moiety224 with a binding polymer 214. The binding polymer 214 can have a freeend 218 or a plurality of free ends 218 that can attach to the reactivemoiety 224 of the reactive dye 220. In embodiments, each of the freeends 218 may be adapted for binding to a single reactive dye 220 or to aplurality of different reactive dyes 220. The polymer-bound dye 210 canbe attached to a particle 216. Optionally a coating or a series ofcoatings (not shown) may be attached to the particle 216, using methodssuch as those described herein. In such cases, the polymer-bound dye 210can be attached to the coating (not shown), as described previously. Insome embodiments, an attachment 228 between the reactive dye 220 and thebinding polymer 214 can be formed first, and then an attachment 230between the polymer-bound dye 210 and the particle 216 or the coatedparticle (not shown) can be formed. In some embodiments, multiple layersof polymer-bound dyes 210 or other polymers (not shown) can be depositedon the particle 216 using the aforesaid methods.

In some embodiments, other components can bind to the polymer couplingagent. Such components can include polymers and other molecules capableof binding with the polymer coupling agent. For instance, when thecoupling agent is a polycation, an anionic component can be adapted tocouple with the polycation. The anionic component can be used to bind toone or more dye components or other entities. Examples of anioniccomponents include a multifunctional entity with a negatively chargedmoiety, a polyanion, and appropriately functionalized multifunctionalcoupling agents as described in the present application (e.g., a silanecoupling agent). Polyanions, such as a cellulosic or starch-basedpolymer, can be advantageously utilized when the coupling agent is apolycation due to the affinity between the polymers. Without being boundby any particular theory, anionic polymers such as cellulosic orstarch-based polymers (e.g., pectin, carboxy methyl cellulose, xanthangum, and the like) can react with a dye component at one or morehydroxyl groups, leaving the acid group free to preserve the anioniccharacter of the polymer. The reaction product can then be precipitatedonto (e.g., electrostatically deposited onto) or otherwise attached to aparticle which has been coated with a polycation such asamine-containing polymer. Polycations can be bound to the fillerparticle using a multifunctional coupling agent or some other mechanismsuch as electrostatic interactions. In related embodiments, alternatinglayers of polycations and dyed polyanions can be repeated applied to afiller particle surface to increase the color intensity if desired.Though these embodiments have been described using dye components boundto the additional component (e.g., polyanion), it is understood thatother types of entities can also be bound such as other polymers orcomponents that can enhance the strength or appearance properties of aresulting paper product.

In some embodiments, a polycation can be applied onto a colored particlesurface, for example as a layer, to enhance interactions with anionicpulp fibers. For instance, a polycation layer can lead to betterretention of fillers and/or pigments in paper products, leading toreduced filler/pigment use during papermaking processes. Also suchpolycations can increase strength properties of the paper product whenincorporated into the pulp sheet relative to not using such polycations.Indeed, these potential advantages are also accrued in other embodimentsof the present invention where a surface-modified filler particleincludes a component (e.g., a polycation) that can interact favorablywith fibers of a paper pulp. The polycation can be a polyamine includingchitosan, branched polyethylenimine, linear polyethylenimine, andpolyallyl amine. The polyamine can be deposited onto the surface of theparticle using electrostatic interactions, spray drying, byprecipitating the polyamine out of solution onto the particle byadjusting the pH, or other suitable techniques. For example, chitosancan be deposited onto the particle by slowly raising the pH untilchitosan is insoluble. In some embodiments, the polycation layer can bethin, e.g., approximately the wavelength of visible light or smaller(less than about 500 nm), such that the color particle surface is notaffected significantly, if at all visually.

Methods for Forming Paper Products with Surface-Modified Pigments

Some embodiments are directed to methods of forming paper products usingsurface-modified pigments described throughout the present application.Papermaking processes, including those understood by one skilled in theart, can be adapted with the teachings herein to practice variousaspects of the invention described herein.

Some embodiments of the invention are directed to methods for producinga paper product (e.g., a paper product with a selected color).Surface-modified pigments, and mixtures for making such pigments, can beproduced such that one or more components bind with filler particles(e.g., a dye component using a coupling agent). Surface-modifiedpigments, and their corresponding mixtures, can be mixed with a pulphaving fibers to make a papermaking dispersion. In some circumstances,the filler particles of the surface-modified pigments can bind to one ormore pulp fibers, resulting in a strengthened paper product and/or onethat retains fines to a larger degree. The dispersion can then be formedinto a sheet of paper or other paper-based material, for example byusing techniques for molding or drawing the dispersion into anappropriate form. The sequence in which such operations are performedcan be in any appropriate manner for forming a papermaking mixture orpaper-based material. For instance, all of the components (such asparticles, coupling agent and dye) can be added in one step to thereactor, while in other embodiments, the particles can be functionalizedwith dye and or other components, and then subsequently added to theother papermaking materials (e.g., pulp and additional fillers etc.).The components of the papermaking mixture include any permutation andcombination of materials as disclosed in the present application.

For uses in the papermaking industry, the compositions and methodsdescribed herein can further include adding other substances to a slurrybefore forming the sheet to boost interactions of the surface-modifiedfiller particles with the pulp fibers. In some embodiments, additivessuch as additional cellulosic or starch polymers or synthetic ionicstrength enhancers may be used. For example polymers such as a cationicstarch can increase the strength of a final paper product. In anotherexample, polyacrylic acid copolymers can be added to aid charge balanceor help retain cationic filler particles and/or surface-modifiedpigments. Wet strength chemicals such as melamine-formaldehyde resins,urea-formaldehyde resins, and epoxidized polyamine-polyamide resins canalso be used. In other embodiments, dyed cellulosic or starch polymerscan be added to impart color and strength to the paper. In embodiments,paper formed according to these compositions and methods can be coatedwith an oppositely charged polymer or with amine reactive polymers toimpart strength, or the paper may be coated with a polymer impartinghydrophobicity or superhydroyphobicity to enhance the product's releasecharacteristics.

Surface-Modified Pigments

Some embodiments of the present invention are directed tosurface-modified pigment particles, which can be added to a papermakingslurry to color a paper product or used in an ink to be applied to apaper. In general, such surface-modified pigments can enhance theappearance or quality of a paper product created by using such apigment, or can result in an ink formulation that can have superiorproperties such as increased affinity for the fibers of paper. In someembodiments, the surface-modified pigments can include pigment particlesthat have a fiber-affinity component bound to the pigment particles.Fiber-affinity components include materials such as polymers, and inparticular polycations as disclosed throughout the present application.For example, a polycation, such as but not limited to chitosan or acationic starch, can be attached or encapsulated onto the particles toform a polycation overcoat on the pigment. A fiber-affinity componentcan be adapted to improve binding of the pigment particles with thefibers of a paper-based product, which can result in the enhancedretention of pigment particles, other fillers, and/or fines during papermaking and/or increased strength of the paper product.

Pigments that can be utilized with the above-described embodimentinclude the range of pigments known to those skilled in the art, as wellas the surface-modified pigments described in the present application.Accordingly, in some embodiments, a pigment particle can comprise atleast one dye component and a coupling agent to bind the dyecomponent(s) to a filler particle. The arrangements and types of fillerparticles, dye components, and coupling agents include all thosedescribed in the various embodiments within the present application. Forexample, the coupling agent can be a multifunctional coupling agent, ora polyelectrolyte. Particular polyelectrolytes include polyelectrolyteshaving an isocyanosilane or another silane. Amine-containing polymers,including but not limited to polyethylenimine, poly(allyl amine),chitosan, and many proteins, can also be used. Amine-containing polymerscan be adsorbed directly to a particle surface, or can be coupledthereto using another coupling agent, as described elsewhere within thepresent application. Free amine groups can be used to tag on dye orinteract with the paper fibers or other paper additives. As well,alternating layers of polyelectrolytes with opposite net charge can beapplied to the particle surface.

Fiber-affinity components, such as a polycation adapted to interact withpulp fibers, can alter the character of the filler particle surface, andcan be used to provide additional functionality. For example, apolycation can be bound with a dye component (e.g., reactive or ionic)to provide a selected coloration to the surface-modified pigment. Thedye component can be bound to the polycation before, after, or duringthe polycation's binding with the filler particle. Colored pigments canalso be further treated with another layer on top (e.g., a biopolymer orpolyanion) of the dyed particle or left as is. Such layering can adaptthe features of any of the embodiments herein particular to adding alayer to a colored pigment.

As previously mentioned, surface-modified pigments particles in accordwith these embodiments can also be used in ink formulations. The inkformulation can include a medium (e.g., an aqueous-based medium) fordispersing the surface-modified pigment particles in which suchparticles provide a selected color to the ink. In one example, silicondioxide nanoparticles functionalized with colored dyes can provide highresolution when used in an inkjet printer. In some embodiments, thepigments can be functionalized with a polycation to interact favorablywith pulp fibers. For instance, chitosan can be precipitated ontoorganic or inorganic pigments. These pigments, which now have a highaffinity for the paper fibers (e.g., cellulose-based fibers), can beused in inks in printers or as fillers to make colored paper.Accordingly, such pigments can be superior to conventional dyes due tolower ink migration once printed on a paper sheet. In addition, such anink formulation can be separated from the pulp during a paper recyclingprocess through addition of salt solution to interrupt the electrostaticinteractions between the polyamine on the particle surface and the pulpfibers. Small particles such as nanoparticles (e.g., having an averagesize of less than 100 nm) can be preferred to achieve a high printresolution. Pigments produced according to these systems and methods canbe useful in a variety of printing processes, including at-homeprinters, office printers and industrial printers.

It is understood by those skilled in the art that colored pigmentsproduced according to these compositions and methods can be added to thepapermaking process stream at any place where filler particles wouldtypically be added. Such pigments may also be added to the paper as acoating step, especially when particles that are normally used in papercoatings form the base particle for subsequent color attachment asdescribed herein.

In other embodiments, surface-modified pigment particles can be furthermodified by agents prior to, or in the paper making stream, with anionicor reactive agents to impart properties such as hydrophobicity. Oneexample of such agents include sizing agents, which can have aliphatic,fluorinated or siloxane reactive chemistries. In further embodiments,particles can be functionalized with polyelectrolytes throughself-assembly of the polyelectrolyte on the surface of the particle orfiber. Subjecting these moieties to either a polymer of opposite chargeto swap ionic character or form multilayers on the surface or byreacting chemistries to the functional groups on the polymer the surfacecharacteristics can easily be altered for use. This process can berepeated by using polyelectrolytes of opposite charges. As in the caseof this and all of the other embodiments, these functionalized and/ordyed particles may interact with the pulp fibers and increase thestrength of the paper, increase particle and fines retention, and reduceamount of materials necessary in the papermaking process.

In any of these embodiments, additional polyanions can be added thatwill further interact electrostatically with the functionalizedparticles. These polyanions may or may not be dyed with reactive dyes.Also, as would be understood by those of skill in the art, the particlesdescribed herein may be added anywhere in the papermaking process. Forexample, the particles can be used as filler or coating, where suchparticles can contribute to enhanced properties in paper, as would beunderstood by those of ordinary skill in the art.

While the present invention has been described in terms of specificmethods, structures, and compositions it is understood that variationsand modifications will occur to those skilled in the art uponconsideration of the present application. As well, the featuresillustrated or described in connection with one embodiment may becombined with the features of other embodiments. Such modifications andvariations are intended to be included within the scope of the presentinvention. Those skilled in the art will appreciate, or be able toascertain using no more than routine experimentation, further featuresand advantages of the invention based on the above-describedembodiments. Accordingly, the invention is not to be limited by what hasbeen particularly shown and described, except as indicated by theappended claims. All publications and references are herein expresslyincorporated by reference in their entirety.

EXAMPLES

The following examples are provided to illustrate some aspects of thepresent application. The examples, however, are not meant to limit thepractice of any embodiment of the invention.

Chemicals used in the following experiments included the following:Chitosan cg110 (Primex, Siglufjodur, Iceland); Softwood(Georgia-Pacific, Neenah, Wis.); Kaolin (Engelhard Corporation (now BASFCatalysts), Iselin, N.J.); 3-aminopropyltrimethoxy silane (Gelest,Morrisville, Pa.); PRO Intense Blue 406 MX reactive dye (Pro Chemical &Dye, Somerset, Mass.); PRO Turkey Red 320 MX reactive dye (Pro Chemical& Dye, Somerset, Mass.); PRO Sun Yellow 108 MX reactive dye (ProChemical & Dye, Somerset, Mass.); PRO Deep Navy 414 MX reactive dye (ProChemical & Dye, Somerset, Mass.); Silicon dioxide (Nanostructured &Amorphous Materials Inc., Los Alamos, N. Mex.); Calcium carbonate(Spectrum Chemicals C1078, Gardena, Calif.); Low methoxy pectin (CPKelcoGenu Pectin (Citrus) Type USP/100, Nijmegen, The Netherlands); Xanthangum (EMD Chemicals XX1110-1; Gibbstown, N.J.); NaOH (Spectrum ChemicalsS1303, Gardena, Calif.); Hydrochloric acid (for chitosan solutions)(Sigma Aldrich 258148, St. Louis, Mo.); Sodium Chloride (for brinesolution) (Sigma Aldrich, St. Louis, Mo.); Isopropyl Alcohol (EMDChemicals PX1834-1, Darmstadt, Germany).

Example 1 Blue Kaolin with Silane Linker

Kaolin pigments that were blue in color were prepared by mixing 20 g ofkaolin particles, 4.0 mL of 3-aminopropyltrimethoxy silane, and 0.8 g ofPRO Intense Blue 406 MX reactive dye into 400 mL of deionized water. Thereaction was allowed to proceed for 4 hours while being stirred. Thereaction product was filtered and (i) washed with water until filtratewas clear; then (ii) washed with brine solution until the filtrate wasclear; then (iii) washed with water to rinse away brine; then (iv)washed with isopropyl alcohol to remove water. The pigments were thenplaced in a 55° C. vacuum oven. After drying overnight, blue pigmentswere obtained.

Example 2 Blue Silica with Silane Linker

Silica pigments that were blue in color were prepared by mixing 20 g ofsilicon dioxide particles (having an average diameter of approximately15 nm), 4.0 mL of 3-aminopropyltrimethoxy silane, and 0.8 g of PROIntense Blue 406 MX reactive dye into 400 mL of deionized water. Thereaction was allowed to proceed for 4 h while being stirred. Thereaction product was filtered and (i) washed with water until filtratewas clear; then (ii) washed with brine solution until the filtrate wasclear; then (iii) washed with water to rinse away brine; then (iv)washed with isopropyl alcohol to remove water. The pigments were thenplaced in a 55° C. vacuum oven. After drying overnight, blue pigmentswere obtained.

Example 3 Red Kaolin with Silane Linker

Kaolin pigments that were red in color were prepared by mixing 20 g ofkaolin particles, 4.0 mL of 3-aminopropyltrimethoxy silane, and 0.8 g ofPRO Turkey Red 320 MX reactive dye into 400 mL of deionized water. Thereaction was allowed to proceed for 4 hours while being stirred. Thereaction product was filtered and (i) washed with water until filtratewas clear; then (ii) washed with brine solution until the filtrate wasclear; then (iii) washed with water to rinse away brine; then (iv)washed with isopropyl alcohol to remove water. The pigments were thenplaced in a 55° C. vacuum oven. After drying overnight, red pigmentswere obtained.

Example 4 Blue Kaolin with Silane Linker and Chitosan Coating

A slurry of blue kaolin particles was created by stirring 5 g ofparticles from Example 1 into 50 mL of deionized water. To this vessel,2.5 mL of a 2.0% CG110 chitosan solution (solution was made bydissolving chitosan into acidic water) was slowly added. To this, 0.1 MNaOH was added until the pH reached 8.

Example 5 Blue Silica with Silane Linker and Chitosan Coating

A slurry of blue silica particles was created by stirring 5 g ofparticles from Example 2 into 50 mL of deionized water. To this vessel,2.5 mL of a 2.0% CG110 chitosan solution (solution was made bydissolving chitosan into acidic water) was slowly added. To this, 0.1 MNaOH was added until the pH reached 8.

Example 6 Blue Kaolin with Chitosan Linker

A slurry of kaolin particles was created by stirring 20 g of kaolin into200 mL of deionized water. To this vessel, 10 mL of a 2.0% CG110chitosan solution (solution was made by dissolving chitosan into acidicwater) was slowly added. To this, 0.1 M NaOH was added until the pHreached 8. To this vessel, 0.8 g of PRO Intense Blue 406 MX reactive dyewas added. The reaction was allowed to proceed for 2 hours while beingstirred. The reaction product was filtered and (i) washed with wateruntil filtrate was clear; then (ii) washed with brine solution until thefiltrate was clear; then (iii) washed with water to rinse away brine;then (iv) washed with isopropyl alcohol to remove water. The pigmentswere then placed in a 55° C. vacuum oven. After drying overnight, bluepigments were obtained.

Example 7 Blue Silica with Chitosan Linker

A slurry of silica particles was created by stirring 20 g of silicondioxide (having an average diameter of approximately 15 nm) into 200 mLof deionized water. To this vessel, 10 mL of a 2.0% CG110 chitosansolution (solution was made by dissolving chitosan into acidic water)was slowly added. To this, 0.1 M NaOH was added until the pH reached 8.To this vessel, 0.8 g of PRO Intense Blue 406 MX reactive dye was added.The reaction was allowed to proceed for 2 hours while being stirred. Thereaction product was filtered and (i) washed with water until filtratewas clear; then (ii) washed with brine solution until the filtrate wasclear; then (iii) washed with water to rinse away brine; then (iv)washed with isopropyl alcohol to remove water. The pigments were thenplaced in a 55° C. vacuum oven. After drying overnight, blue pigmentswere obtained.

Example 8 Blue Calcium Carbonate with Chitosan Linker

A slurry of calcium carbonate particles was created by stirring 20 g ofcalcium carbonate into 200 mL of deionized water. To this vessel, 10 mLof a 2.0% CG110 chitosan solution (solution was made by dissolvingchitosan into acidic water) was slowly added. The high pH of the calciumcarbonate solution caused the chitosan to precipitate onto the calciumcarbonate particles. To this vessel, 0.8 g of PRO Intense Blue 406 MXreactive dye was added. The reaction was allowed to proceed for 2 hourswhile being stirred. The reaction product was filtered and (i) washedwith water until filtrate was clear; then (ii) washed with brinesolution until the filtrate was clear; then (iii) washed with water torinse away brine; then (iv) washed with isopropyl alcohol to removewater. The pigments were then placed in a 55° C. vacuum oven. Afterdrying overnight, blue pigments were obtained.

Example 9 Blue Calcium Carbonate with Chitosan Linker and ChitosanCoating

A slurry of blue calcium carbonate was created by stirring 5 g ofparticles from Example 8 into 50 mL of deionized water. To this vessel,2.5 mL of a 2.0% CG110 chitosan solution (solution was made bydissolving chitosan into acidic water) was slowly added.

Example 10 Blue Low Methoxy Pectin

Blue low methoxy pectin was prepared by first adding 0.5 g of lowmethoxy pectin to 100 mL of deionized water. NaOH was then added tobring the pH up to 8.0 before adding 0.2 g of PRO Deep Navy 414 MXreactive dye. The reaction was left for one hour. The dyed pectinsolution was then poured into a large volume of acetone where the dyedpectin precipitated out of the solution. The dyed pectin was then washed3× with acetone to remove any unreacted dye. After drying overnight in a55° C. vacuum oven, a polymer blue in color was obtained.

Example 11 Yellow Low Methoxy Pectin

Yellow low methoxy pectin was prepared by first adding 0.5 g of lowmethoxy pectin to 100 mL of deionized water. NaOH was then added tobring the pH up to 8.0 before adding 0.2 g of PRO Sun Yellow 108 MXreactive dye. The reaction was left for one hour. The dyed pectinsolution was then poured into a large volume of acetone where the dyedpectin precipitated out of the solution. The dyed pectin was then washed3× with acetone to remove any unreacted dye. After drying overnight in a55° C. vacuum oven, a polymer yellow in color was obtained.

Example 12 Blue Xanthan Gum

Blue xanthan gum was prepared by first adding 0.5 g of xanthan gum to100 mL of deionized water. NaOH was then added to bring the pH up to 8.0before adding 0.2 g of PRO Deep Navy 414 MX reactive dye. The reactionwas left for one hour. The dyed xanthan gum solution was then pouredinto a large volume of acetone where the dyed pectin precipitated out ofthe solution. The dyed xanthan gum was then washed 3× with acetone toremove any unreacted dye. After drying overnight in a 55° C. vacuumoven, a polymer blue in color was obtained.

Example 13 Blue Calcium Carbonate with Chitosan and Pectin

A slurry of calcium carbonate particles was created by stirring 5 g ofcalcium carbonate into 50 mL of deionized water. To this vessel, 2.5 mLof a 2.0% CG110 chitosan solution (solution was made by dissolvingchitosan into acidic water) was slowly added. The high pH of the calciumcarbonate solution caused the chitosan to precipitate onto the calciumcarbonate particles. To this, 15 mL of a 2.5% blue-dyed pectin solution(obtained by dissolving polymer from Example 10 in water) was added. Thecontents were filtered and washed with water until filtrate was clear.The pigments were then placed in a 80° C. vacuum oven. After dryingovernight, blue pigments were obtained.

Example 14 Pulp Slurry

A 5% slurry was prepared by blending 20 g refurnished softwood in 400 mLof water. The slurry was diluted to 0.5% pulp by adding 3.6 L of water.

Example 15 Pulp with Chitosan and Blue Pectin Slurry

A vessel was filled with 1 L of the pulp slurry prepared in Example 14.To this vessel, 2.5 mL of a 2.0% CG110 chitosan solution (solution wasmade by dissolving chitosan into acidic water) was slowly added. Tothis, 0.1 M NaOH was added until the pH reached 8. To this, 50 mL of a2.5% blue-dyed low methoxy pectin solution (obtained by dissolvingpolymer from Example 10 in water) was added.

Example 16 Handsheet Preparation

Handsheets were prepared using a Mark V Dynamic Paper Chemistry Jar andHand-Sheet Mold from Paper Chemistry Laboratory, Inc. (Larchmont, N.Y.).The appropriate volume of 0.5% pulp slurry was mixed with theappropriate volume of pigment slurry. This combined slurry was dilutedwith water up to 2 L and added to the handsheet maker. The slurry wasmixed at a rate of 1100 RPM for 5 seconds, 700 RPM for 5 seconds, and400 RPM for 5 seconds. The water was then drained off. The subsequentsheet was then transferred off of the wire, pressed and dried.

Example 17 Paper with Blue Kaolin

Two handsheets were produced according to the method of Example 16 using240 mL of the material from Example 14 and 0.6 of pigment from Example 1(pigment was first dispersed in 20 mL of water). The resultinghandsheets were blue in color.

Example 18 Paper with Red Kaolin

Two handsheets were produced according to the method of Example 16 using240 mL of the material from Example 14 and 0.6 of pigment from Example 3(pigment was first dispersed in 20 mL of water). The resultinghandsheets were red in color.

Example 19 Paper with Blue Kaolin Coated with Chitosan

Two handsheets were produced according to the method of Example 16 using240 mL of the material from Example 14 and 0.3 of pigment from Example 4(pigment was first dispersed in 20 mL of water). The resultinghandsheets were blue in color.

Example 20 Paper with Blue Calcium Carbonate

Two handsheets were produced according to the method of Example 16 using240 mL of the material from Example 14 and 0.6 of pigment from Example 8(pigment was first dispersed in 20 mL of water). The resultinghandsheets were blue in color.

Example 21 Paper with Blue Calcium Carbonate Coated with Chitosan

Two handsheets were produced according to the method of Example 16 using240 mL of the material from Example 14 and 0.3 of pigment from Example 9(pigment was first dispersed in 20 mL of water). The resultinghandsheets were blue in color.

Example 22 Paper with Blue Low Methoxy Pectin

Two handsheets were produced according to the method of Example 16 using300 mL of the material from Example 15. The resulting handsheets wereblue in color.

EQUIVALENTS

While specific embodiments of the subject invention have been discussed,the above specification is illustrative and not restrictive. Manyvariations of the invention will become apparent to those skilled in theart upon review of this specification. The full scope of the inventionshould be determined by reference to the claims, along with their fullscope of equivalents, and the specification, along with such variations.

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in this specification and attached claimsare approximations that may vary depending upon the desired propertiessought to be obtained by the present invention.

1. A colored paper product, comprising: pulp comprising a plurality offibers; and surface-modified pigment particles imparting color to thepaper product, the surface-modified pigment particles comprising: (i) afiller particle embedded within the pulp, (ii) at least one dyecomponent adapted to provide a selected color to the paper product, and(iii) a coupling agent binding the at least one dye component and thefiller particle together.
 2. The colored paper product of claim 1,wherein the coupling agent is directly bound to the filler particle byat least one of covalent bonding, non-covalent bonding, electrostaticforces, Van der Waals forces, hydrogen bonding, and intermolecularforces.
 3. The colored paper product of claim 1, wherein the pulpcomprises cellulosic-based fibers.
 4. The colored paper product of claim1, wherein the filler particle of the surface-modified pigment particlescomprises at least one of a biopolymer, a bio-oligomer, metal oxide,silaceous material, and calcium carbonate.
 5. The colored paper productof claim 1, wherein the filler particle of the surface-modified pigmentparticles comprises an inorganic surface.
 6. The colored paper productof claim 5, wherein the inorganic surface comprises at least one ofcalcium carbonate, kaolin, and titanium dioxide.
 7. The colored paperproduct of claim 5, wherein the inorganic surface of thesurface-modified pigment particles comprises sites attached to thecoupling agent by reaction of a hydroxide group of the inorganicsurface.
 8. The colored paper product of claim 1, wherein the couplingagent comprises a silane group reacted to attach the coupling agent andthe filler particle together.
 9. The colored paper product of claim 8,wherein the coupling agent further comprises a reactive group includingat least one of an acrylate, an amine, an amino, a carboxyl, a thiol, anepoxy, an isocyano group, and a hydroxyl, the reactive group reacted tobind the reactive group and the filler particle together.
 10. Thecolored paper product of claim 1, wherein the coupling agent comprises apolyelectrolyte.
 11. The colored paper product of claim 10, wherein thepolyelectrolyte comprises a polycationic polymer.
 12. The colored paperproduct of claim 11, wherein the polycationic polymer comprises at leastone of an amine-containing polymer and a cationic starch.
 13. Thecolored paper product of claim 12, wherein the amine-containing polymercomprises at least one of chitosan, polyalkyleneimine, polyvinyl amine,and polyallyl amine.
 14. The colored paper product of claim 11, furthercomprising: an anionic component adapted to couple the anionic componentand the polycationic polymer together.
 15. The colored paper product ofclaim 14, wherein the anionic component is adapted to bind the at leastone dye component and the polycationic polymer together.
 16. The coloredpaper product of claim 15, wherein the anionic component is a polyanion.17. The colored paper product of claim 15, wherein the anionic componentcomprises another coupling agent including a silane group.
 18. Thecolored paper product of claim 1, wherein the at least one dye componentcomprises at least one of halogenotrizine, carboxypyridinium-substitutedtriazine, trihalogenopyrimidine, dichloroquinoxaline, vinyl sulfone,halotriazine, anthraquinone-like structure, azo dye, triaryl dye, andmetal complex.
 19. The colored paper product of claim 1, wherein the atleast one dye component comprises at least one of a fluorescent dye, aphosphorescent dye, a photochromic dye, a thermochromic dye, a FD&C dye,a whitener, a brightener, a light stabilizer, and an ultraviolet lightstabilizer.
 20. The colored paper product of claim 1, wherein thesurface-modified pigment particles are adapted so that at least onesurface-modified pigment particle and at least one fiber of the pulp arebound together.
 21. The colored paper product of claim 20, wherein thesurface-modified pigment particles include coupling agent binding thefiller particle and at least one fiber of the pulp together.
 22. Thecolored paper product of claim 20, wherein the surface-modified pigmentparticles further comprise a functionalizing polymer binding the fillerparticle and at least one fiber of the pulp together.
 23. The coloredpaper product of claim 22, wherein the functionalizing polymer and thecoupling agent are attached together.
 24. The colored paper product ofclaim 23, wherein the functionalizing polymer and the coupling agent aredirectly attached together.
 25. The colored paper product of claim 22,wherein the functionalizing polymer and the filler particle are boundtogether by at least one of covalent bonding, non-covalent bonding,electrostatic forces, Van der Waals forces, hydrogen bonding, andintermolecular forces.
 26. The colored paper product of claim 22,wherein the functionalizing polymer comprises at least one of anamine-containing polymer, a glycoaminoglycan, an amino-containingpolymer, and an imine-containing polymer.
 27. The colored paper productof claim 1, wherein the surface-modified pigment particles furthercomprise an intermediary component binding the coupling agent and fillerparticle together.
 28. The colored paper product of claim 1, wherein thesurface-modified pigment particles further comprise an intermediarycomponent binding the coupling agent and the at least one dye componenttogether. 29-54. (canceled)
 55. A method of producing a colored paperproduct, comprising: producing a surface-modified pigment by bindingfiller particles and at least one dye component together using acoupling agent; mixing the surface-modified pigment with pulp comprisinga plurality of fibers to produce a papermaking dispersion; and formingthe colored paper product using the papermaking dispersion.
 56. Themethod of claim 55, further comprising: binding the filler particles andat least one fiber of the pulp together.
 57. The method of claim 55,wherein the step of producing the surface-modified pigment begins beforethe step of mixing the surface-modified pigment with pulp.
 58. Themethod of claim 55, wherein the steps of producing the surface-modifiedpigment and mixing the surface-modified pigment with pulp occursubstantially simultaneously.
 59. The method of claim 55, wherein thestep of producing the surface-modified pigment comprises adjusting colorof the paper product by selecting the amount of coupling agent relativeto the at least one dye component.
 60. The method of claim 55, whereinthe step of producing the surface-modified pigment comprisesencapsulating the filler particles with a polycation.
 61. The method ofclaim 60, wherein the step of encapsulating the filler particlescomprises attaching the polycation and the filler particles togetherwith the coupling agent.
 62. The method of claim 60, wherein thepolycation is the coupling agent.
 63. The method of claim 62, furthercomprising: coupling the at least one dye component and the polycationtogether before encapsulating the filler particles with the polycation.64. The method of claim 60, wherein the step of encapsulating the fillerparticles comprises self assembling the polycation on a surface of thefiller particles.
 65. The method of claim 60, further comprising:binding an anionic component to the polycation.
 66. The method of claim55, wherein the coupling agent comprises a silane group. 67-76.(canceled)